custome button in pagelayout to check filed condtion then it link to your visualforce page visualforce page

{!REQUIRESCRIPT("/soap/ajax/20.0/connection.js")}
{!REQUIRESCRIPT("/soap/ajax/20.0/apex.js")}

var s="{!nnr__c.Application_Status__c}";
var p="{!nnr__c.Application_Category__c}";

if(s=='Sanctioned' && p==' Group') {
window.open("/apex/yourVFPAGE?id={!Application__c.Id}");
}
else {
alert("Insufficient privileges, You are not authorized to download the application.");

}